let's be real here. there are a few issues with simply looking at their regular season record to measure organizational success. First of all, as we all know winning regular season games & winning playoff series are two different animals. Cassidy learned very well from Julien how to scrape out regular season wins even with roster limitations. There's nothing wrong with that at all; in fact it's an important trait for a team to have, but it doesn't necessarily translate to playoff success.
second of all, the Bruins are still largely dependent on several guys over the age of 30. Chara & Bergeron are just freaks of nature. It's highly unusual to get that level of play out of guys their age. Marchand, Rask & Krejci are also better than most guys in their age group. I'd say Krug, Pasta, McAvoy, Carlo & Debrusk round out the rest of their core. So yes they've had some success with drafting & developing, but at least half of the team's success in the immediate past has been from guys who have been on the team for years and are vastly outperforming expectations for guys in their age brackets. The only guy in that list who is statistically in his prime is Krug.
The point I'm trying to make is that yeah the Bruins have been a consistently good team over the past 2 seasons and that obviously speaks to them doing a lot of things right, but that success can only partially be attributed to the drafting & development of the current management group.
They've done a terrific job drafting & developing defensemen, but their track record drafting & developing forwards in the Sweeney years is pretty spotty at best. Debrusk is Sweeney's one big win and even in that case they arguably missed out on better players to draft him. Heinen was not a Sweeney pick but I'll give them credit for developing him, although he still hasn't found a consistent top 6 rhythm yet. Donato was arguably the best forward prospect they had not in the NHL and they traded him. Studnicka, Frederic, Steen, Lauzo & Senyshyn have interesting skillsets, but none of them are locks to be productive top 6 NHL forwards.
So yes they're doing a lot of things right in the day to day NHL grind & have the record to prove it but a LOT of that is due to unusual longevity from their veteran forwards & a very deep D corps combined with terrific coaching. Drafting & developing skill forwards in the Sweeney era absolutely leaves something to be desired, I don't know how you or anyone can dispute that.